My CPU is still faster than my GPU
Increase your tile size.



Your CPU is like Usain Bolt, and your GPU is a lot of turtles. Enough turtles will cover more total distance travelled than Usain Bolt going at full speed within the same time.

Likewise, your GPU will process more pixels at the same time, although slower, so increase the tile size.

You will need to experiment, though, with various values. You will need to find that sweet spot for your GPU and scene. If your values are too high, your GPU might not have enough cores to process an entire tile in one shot, so you might get that lag.

UPDATE

Your GPU has 96 cores running at 700 MHz. This explains why you may not be getting a very big GPU benefit no matter how you tweak the tile size.

In comparison, today's latest budget NVidia GPU is the GTX 950, which has 768 cores, running at a slightly higher 1024 MHz.

I advise you to upgrade your GPU.